1. Field of the Invention
The invention relates to membrane control, and, in particular, to an electrode configuration for electrostatically controlling the shape of a membrane used in adaptive optics to correct distortion of optical signals.
2. Description of the Related Art
Membranes, such as optical membranes, can serve as mirrors, light gathering and focusing devices, etc. A membrane whose surface can be deformed may serve as an adjustable mirror, which may be useful for such applications as focusing, and for correcting aberrations that may occur as a result of, e.g., light passing through atmosphere, the latter of which may be problematic in astronomical observations using a telescope.
A membrane device may employ one or more actuators to change the shape of the membrane surface. A membrane device that can be selectively actuated in opposing directions to effect a deformation of the membrane surface first via a deforming force, and then via an opposing, restoring force to restore the original shape of the membrane, is highly desirable for use as an adaptive optical element.
Traditional membrane devices operate via electrostatic attraction of the membrane surface to one or more electrodes located beneath the membrane. Due to the lack of an opposing upward electrostatic restoring force, these devices have limited capability.
Some membrane devices, such as those described in U.S. Pat. No. 6,639,710, implement such a restoring force by a transparent bias electrode, which is placed in the optical path above the membrane. These devices may suffer from loss of optical power due to absorption or scattering by the bias electrode, which is typically transparent for only a limited range of wavelengths. U.S. Pat. No. 6,639,710 also suggests using a circular electrode ring for the restoring electrode, but such a ring will not provide a sufficiently uniform electric field over the area of the membrane.